1. Field of the Invention
The present invention relates to a throttle valve control device. In particular, the present invention relates to a throttle valve control device that detects an amount of opening degree of a throttle valve, which is provided within an intake pipe of an engine used in an automobile, to perform feedback control of the throttle valve to a position having a desired opening degree by using a throttle actuator.
2. Description of the Related Art
In a conventional throttle abnormality detection device in an internal combustion engine, for detecting return spring abnormalities of a throttle actuator, a throttle controlling means controls an opening degree of the throttle valve using a DC motor based on an amount that an accelerator pedal is pressed. Actual torque that the motor generates is detected by a torque detecting means, and an amount of fluctuation in the torque is detected for every given period of time by a fluctuation amount detecting means. If the amount of fluctuation in the torque is equal to or less than a given value, it is judged that there is breakage to the return spring of the throttle valve (refer to JP 08-270487, for example).
In general, in an electronic throttle system having a return spring and a DC motor as sources for return energy, if a frictional torque of a throttle valve drive system changes greatly (increase) due to breakage of the return spring of the throttle valve, throttle valve tracking characteristics (responsiveness) for throttle valve operations in response to accelerator pedal operations by a driver will deteriorate. An engine driving force may develop against the intention of the driver, which is extremely undesirable.
Further, if the frictional torque of the throttle valve driver system does not change greatly due to the breakage of the return spring of the throttle valve, the tracking characteristics for the throttle valve operations in response to the accelerator pedal operations by the driver are secured. Conversely, if there is an abnormality in an electric system of the DC motor, such as a breaking of wires of the DC motor terminals, while the driver presses the accelerator into a fully opened state, there is no energy sources for returning the throttle valve even if the accelerator pedal is returned to a fully closed position. As a result, the throttle valve stays in the fully opened position, and an engine driving force may develop against the intention of the driver, which is extremely undesirable.
In the conventional throttle abnormality detection device described above, the torque generated by the DC motor is detected, and compares the amount of fluctuation in the torque detected for every given period of time with a given value, thus performing abnormality judgment on the throttle valve. However, there are large fluctuations in the torque of a throttle valve shaft itself during engine operation, such as: changes in torque constant of the DC motor due to individual differences in the torque characteristics of the throttle shaft of the throttle actuator and temperature changes (reduction in magnet force of permanent magnetism); changes in viscous resistance of a lubricant in a speed reduction gear portion; transient contaminants that engage in between a valve and a bore; and changes over time in an amount of adhered sludge. As a result, misjudgments tend to occur for the above-mentioned cases. In addition, there occurred such problems that the detection precision became worse, etc. when the given value used in the judgments is made larger in order to avoid the misjudgments.